The police officers who first responded to the scene of the explosion in"saved lives" with their quick actions, the city's police chief said, as federal investigators continue to search for clues. Six officers initially responded to a report of shots fired Friday when they encountered a blaring a recorded warning that a bomb would detonate in 15 minutes, Metro Nashville Police Chief John Drake said.
Police evacuated nearby buildings and called in the bomb squad. The RV exploded shortly afterward, Drake said.
"They immediately began knocking on doors, not knowing when the bomb would go off," Drake said at a press conference Friday night. "They didn't think of themselves...they thought of the citizens of Nashville. They saved lives today, and their heroism should be noted."
CBS affiliate WTVF-TV reports police identified the six officers as: Officer Brenna Hosey, Officer James Luellen, Officer Michael Sipos, Officer Amanda Topping, Officer James Wells and Sergeant Timothy Miller.
Mayor John Cooper commended the officers' bravery.
"They took swift action, directed people away, even when their own lives were in peril. This is a year we understand what first responders mean to our community time and time again."
The Tennessean reported that a dog walker was heading towards the vehicle just before the explosion, but police sent him back in the other direction, potentially saving him from injury or death.
The blast knocked an officer to the ground, the paper said, and gave another officer hearing loss.
Police believe the blast was intentional but don't yet know a motive or target, and Drake noted that officials had not received any threats before the explosion.
The chief said investigators at the scene "have found tissue that we believe could be remains, but we'll have that examined and let you know at that time." Police could not say whether it potentially came from someone inside the RV.
Three people taken to area hospitals for treatment were in stable condition Friday evening, Cooper said.
Surveillance video published on a Twitter account Friday that appeared to be across the street from the blast captured the warning issuing from the RV, "... if you can hear this message, evacuate now," seconds before the explosion.
The blast sent black smoke and flames billowing from the heart of downtown Nashville's tourist scene, an area packed with honky-tonks, restaurants and shops. Buildings shook and windows shattered streets away from the explosion near a building owned by AT&T that lies one block from the company's office tower, a landmark in downtown.
"We do not know if that was a coincidence, or if that was the intention," police spokesman Don Aaron said. He said earlier that some people were taken to the department's central precinct for questioning but declined to give details.
AT&T said the affected building is the central office of a telephone exchange, with network equipment in it. The blast interrupted service, but the company declined to say how widespread outages were.
The Associated Press contributed to this report.